Physiological systems control the fluidity of blood in mammals [Majerus, P. W. et al: Anticoagulant, Thrombolytic, and Antiplplatelet Drugs. In Hardman, J. G. and Limbird, L. E., editors: Goodman & Gilman's The Pharmacological Basis of Therapeutics. 9th edition. New York, McGraw-Hill Book Co., 1996, pp. 1341–1343]. Blood must remain fluid within the vascular systems and yet be able to undergo hemostasis, cessation of blood loss from a damaged vessel, quickly. Hemostasis or clotting begins when platelets first adhere to macromolecules in subendothelian regions of an injured and/or damaged vessels. These platelets aggregate to form the primary hemostatic plug and stimulate local activation of plasma coagulation factors leading to generation of a fibrin clot that reinforces the aggregated platelets.
Plasma coagulation factors include factors II, V, VII, VIII, IX, X, XI, and XII; these are also called protease zymogens. These coagulation factors or protease zymogens are activated by serine proteases leading to coagulation in a so called “coagulation cascade” or chain reaction [Handin, R. I.: Bleeding and Thrombosis. In Wilson, J., et al. editors: Harrison's Principles of Internal Medicine. 12th Edition, New York, McGraw-Hill Book Co., 1991, p. 350]. Coagulation or clotting occurs in two ways through different pathways. An intrinsic or contact pathway leads from XII to XIIa to Ma to IXa and to the conversion of X to Xa. Xa with factor Va converts prothrombin (II) to thrombin (IIa) leading to conversion of fibrinogen to fibrin. Polymerization of fibrin leads to a fibrin clot. An extrinsic pathway is initiated by the conversion of coagulation factor VII to VIIa by Xa The presence of Tissue Factor and VIIa accelerates formation of Xa in the presence of calcium ion and phospholipids. Formation of Xa leads to thrombin, fibrin, and a fibrin clot as described above. The presence of one or more of these many different coagulation factors and two distinct pathways of clotting could enable the efficacious, selective control and better understanding of parts of the coagulation or clotting process.
While clotting as a result of an injury to a blood vessel is a critical physiological process for mammals such as man, clotting can also lead to disease states. A pathological process called thrombosis results when platelet aggregation and/or a fibrin clot blocks (i.e., occludes) a blood vessel. Arterial thrombosis may result in ischemic necrosis of the tissue supplied by the artery. When the thrombosis occurs in a coronary artery, a myocardial infarction or heart attack can result. A thrombosis occurring in a vein may cause tissues drained by the vein to become edematous and inflamed. Thrombosis of a deep vein may be complicated by a pulmonary embolism. Preventing or treating clots in a blood vessel may be therapeutically useful by inhibiting formation of blood platelet aggregates, inhibiting formation of fibrin, inhibiting thrombus formation, inhibiting embolus formation, and for treating or preventing unstable angina, refractory angina, myocardial infarction, transient ischemic attacks, atrial fibrillation, thrombotic stroke, embolic stroke, deep vein thrombosis, disseminated intravascular coagulation, ocular build up of fibrin, and reocclusion or restenosis of recanalized vessels.
There have been several reports of non-peptidic and peptidic compounds that act as an inhibitor of a coagulation factor present in the coagulation cascade or clotting process. In PCT Patent Application WO 97/40024, Sanderson et al. describe alkyl, cycloalkyl, and trifluoromethyl substituted pyrazinones reported to inhibit thrombin activity. In PCT Patent Application WO 98/08840, Duggan et al. describe 2-heterocyclylacetyl derivatives of β-alanine esters reported to inhibit αvβ3 and αvβ5 receptors and possess utility in atheriosclerosis. In PCT Patent Application WO 98/09949, Suzuki et al. describe 2-heterocyclylacetamido derivatives of 1,2-diketones and report that they inhibit proteases, especially chymase inhibitors. In PCT Patent Application WO 98/42342, Isaacs et al. describe additional alkyl, cycloalkyl, and trifluoromethyl substituted pyrazinones reported to inhibit human thrombin. In PCT Patent Application WO 99/61442, Sanderson and Naylor-Olsen describe 1-(5-methylenecarboxamidomethyleneimidazo-[1,2-a]pyridinyl) pyrazinones without substitution in the imidazolyl portion and reported that the compounds inhibit thrombin activity. In PCT Patent Application WO 99/59591, Sanderson et al. describe 1-((N-substituted aminopyridyl and N-substituted phenyl)amidocarbonylmethylene)pyrazinones reported to inhibit thrombin. In PCT Patent Application WO 99/64446, Lu et al. describe 1-((N-amidinoaminooxyalkylene and N-amidinohydrazinoalkylene) amidocarbonylmethylene)pyrazinones reported to inhibit trypsin-like serine proteases and thrombin. In Japanese Patent Application 99/229491, Black et al. describe thrombin inhibiting halo and alkyl substituted pyrazinone acetamides in which the amide nitrogen is substituted by a group containing a benzimidazole or indole ring.